In the 1970s, researchers discovered that polymer-salt complexes could serve as excellent electrolytes for solid state battery cells. In such a cell, the polymer is the electrolytic medium through which lithium cations are carried from a metallic lithium anode to a cathode composed of an intercalating material, such as titanium disulfide. The presence of a potential difference between the anode and the cathode of the polymeric cell produces an electric current through a load that is connected to the battery. There are several benefits associated with the use of a polymeric material as an electrolytic medium. Specifically, a polymer of this type is typically a non-volatile, non-corrosive, solid, and flexible material that may be easily processed into thin films and/or intricate shapes.
Almost since the discovery of polymer batteries, scientists have been conducting research into their possible uses. The minimal toxicity, lightweight, flexibility, and excellent energy storage capacity of polymer batteries has spurred development of their use in medical applications. One such application has been to provide electrical power to energize implanted pacemakers and defibrillators. There is much less concern about the toxicity of polymer batteries for such uses than more conventional Ni-Cd, or metallic hydride rechargeable batteries. Furthermore, polymer batteries can be fabricated with a minimal amount of metal, which avoids undesirable imaging artifacts that are often caused by implanted metal objects within a patient's body. Since polymer batteries are flexible, they can be distorted without damage, for example, to facilitate their insertion into a patient's body through a small incision.
Other medical applications for polymer battery power sources are likely to be developed. A prospective application of this technology that apparently has not yet been considered is providing power to energize implanted light sources to render light therapy. One type of light therapy, which is referred to as photodynamic therapy (PDT), is carried out after a photoreactive agent is administered to a patient. The photoreactive agent is preferentially absorbed by abnormal tissue at a treatment site, e.g., a tumor, rather than normal tissue. Light from a laser or other light source is administered to the treatment site to destroy the abnormal tissue. It is believed that the light absorbed by the sensitized abnormal cells that have absorbed the photoreactive agent produces singlet oxygen, which destroys the tumor cells.
Commonly assigned U.S. Pat. No. 5,445,608 discloses various embodiments for implanted probes that emit relatively low intensity light to administer PDT, and commonly assigned U.S. Pat. No. 5,800,478 discloses several embodiments for implantable flexible circuits on which light sources for administering PDT are mounted. The specification and drawings of both U.S. Pat. Nos. 5,445,608 and 5,800,478 are hereby specifically incorporated herein by reference. As disclosed in these two patents, the electrical current required to energize the LEDs or other light sources on the implanted probes can be provided from an external source coupled electromagnetically to an implanted receiver coil, or can be provided by a conventional storage battery that is implanted with the probe. Using a storage battery as a source of the electrical current energizing an implanted light probe or other medical device is preferable to providing the power at a fixed location to permit a patient to be mobile. Also, it may be preferable to employ a rechargeable battery if the PDT will likely continue for a very long period of time, to enable the therapy to continue without requiring further invasive procedures. However, conventional storage batteries represent a potential toxicity risk, are relatively heavy, and include metallic components that are undesirable when it is necessary to produce images of the patient's body using magnetic resonance imaging (MRI), or other imaging paradigms.
Accordingly, it would be desirable to energize light emitting sources (and other implanted medical devices) with polymer batteries to benefit from the lightweight, minimal metal content, and low risk of toxicity characteristics of such batteries. Moreover, polymer batteries can provide other functions and benefits not achievable with conventional batteries. For example, a flexible polymer battery can serve the purpose of a battery and its electrodes can serve as conductors extending between an implanted electromagnetic receiver and a medical device. A polymer battery can provide support for light sources or other electronic devices mounted in spaced-apart array on conductive traces applied to a flexible sheet. Further, a flexible polymer battery should provide heat sink capabilities, dissipating heat produced by light sources and other electronic devices. Because of the low toxicity of polymer batteries, they are ideal for inclusion in implanted capsules or beads designed to provide medical therapy, which may remain in a patient's body for an extended period of time.